Detailed design simulation may not eliminate all axial compressor blade failures as some of these failures can be a result of interaction between different components and therefore difficult to predict. One such failure mode is tip corner cracking that occurs towards the trailing edge of a blade due to Chord-Wise bending mode excitation. It is understood that the failure may be a result of resonance of the vanes passing frequency, which is the frequency of the vanes' wakes impacting an adjacent blade, and the chord-wise bending, which relates to a particular blade's Eigen-frequency. This can be characterised by a local bending of the tip of the blade in a direction perpendicular to the blade's chord. Another assumed failure cause can be a forced excitation resulting from rubbing of the blade's tip against the compressor casing. This rubbing can occur wherever new blades are mounted in a compressor.
Known solutions to tip corner cracking can include increasing the number of vanes. While this can be effective in eliminating a particular resonance, the solution can increase manufacturing cost and reduces stage efficiency and further does not address the problem of rubbing.
Another solution can involve increasing the blade's clearances at the tip, thereby reducing the rubbing potential. This however can reduce stage efficiency and may negatively affect the surge limit.
A further solution can involve changing the blade design by introducing squealer tips or abrasive coating, for example as described in U.S. Pat. No. 6,478,537 B2 as it relates to turbine blades, and/or using a hardened material on the blade's tip, as described in U.S. Patent Application Publication No. 2008/0263865 A1.
In each case disclosed above, manufacturing costs can be increased. In addition, the foregoing solutions do not always address tip corner cracking.